Cannabinoid Drug Interactions

The drug interaction information provided in this section is a compilation of published literature, including clinical trials and case reports and may include interpretation¹ by PCCC.

Additional information regarding theoretical drug interactions is also presented and is based on our evaluation of the potential for harm if such an interaction were to occur.

Criteria considered:

• Hepatic metabolism of the victim drug
• Cytochrome P450 involvement
• Drugs with a narrow therapeutic window
• Dose, frequency, and route of cannabis use

Antithrombotic Agents

Warfarin

Description

In several published case reports, warfarin has been associated with increases in INR when used in conjunction with THC and CBD, both in oral and inhaled formulations.

Dosing most likely is a factor when predicting an interaction. One case report described a patient on warfarin who added a low dose of oromucosal THC/CBD resulting in no INR fluctuations (Thomas 2022)

Several case reports have been published describing increased INR in patients using various formulations of cannabis, including high-dose oral CBD as well as smoked and oral THC products. While there are some inconsistencies and confounding variables amongst the reports, warfarin has a narrow therapeutic range; therefore, it is prudent to inquire about CBD/THC use in patients who are on warfarin.

Mechanism

THC & CBD inhibition of CYP 2C9 metabolism of S-warfarin (and/or inhibition of CYP 3A4 metabolism of R-warfarin), resulting in higher drug concentrations of warfarin

Evidence

Hsu et al 2020

Cortopassi 2020

Damkier et al 2018

Grayson et al 2017

Yamreudeewong et al 2009

Thomas et al 2022

Direct Oral Anticoagulants (DOACS)